Carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) concentrations of ice samples from a South American mountain glacier are larger than those in coeval polar ice cores. Of the six possible mechanisms that may cause the composition of air measured in ice cores to depart from that of the overlying troposphere (gravitational fractionation, thermal fractionation, gases trapped in refrozen meltwater, atmospheric heterogeneity, abiotic chemical reactions, and biologically mediated chemical reactions), only metabolism of a consortium of microorganisms within the ice can explain our data.

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